The present exemplary embodiments are related to reprinting. Embodiments include methods and systems for producing reprints of a document with improved consistency relative to a reference printing of the document. For the most part, the methods and systems will be described in regard to color consistency and xerographic or electrophotographic systems. However, embodiments can address other printing issues, such as, for example, image size and gloss and in and between other marking systems, such as, for example, thermal or piezo inkjet printing systems.
In order to take advantage of the economies of —just-in-time—manufacturing, it has become common to produce short runs of documents or print jobs and to —reprint—additional copies of the document or print job on an as-needed basis. This has raised issues regarding consistency between a first or selected reference printing and subsequent reprints of the same document or print job. There are many factors that have an influence on the appearance of, for example, the color of a printed document. For instance, the performance of certain printing system components changes with age. Consumable materials, such as, inks and toners, are replaced with inks or toners from different batches or lots. Worn mechanical components may also be replaced. Print media, such as, paper or velum, may be replaced with paper from different production lots, different manufacturers and be of different grades and quality. All of these factors can influence a perceived consistency between, for example, the appearance of color images in a second or reprint printing of a document as compared to a first or reference printing of that document.
In an effort to achieve a color or appearance requested by a customer, a printing system operator may change or adjust a state of a printing system away from a calibrated or reference state. For example, through an iterative proofing process, a printing system operator may drive a printing system away from a calibrated state in order to reach or produce a color or appearance that cannot be achieved by the printing system in its normal or nominal calibration configuration.
The printing system operator may adjust calibration or transformation information that translates color descriptions into colorant amount or density requests. Additionally, or alternatively, the operator may adjust the state of controls or parameters (i.e., machine or system state data) associated with the printing system, such as, for example, the set points and parameters associated with the imaging process of the printing system.
For instance, some xerographic or electrophotographic systems include a hierarchical control scheme. Note: as used herein, xerographic and electrophotographic are essentially equivalent terms and are both used to refer to powder based and liquid based marking technologies. An illustrative xerographic system includes level 1 controls for maintaining electrophotographic actuators at set points, level 2 controls for selecting set points for the level 1 control loops and level 3 controls for compensating for residual differences between actual and target values of aspects of the electrophotographic process.
For example, in some xerographic systems, available actuators can include cleaning field strength or voltage, development field strength or voltage, imager or laser power and an AC wire voltage associated with some developers. For instance, in some xerographic environments, level 1 control loops include electrostatic volt meters (ESV) for measuring charge voltage generated by charge applied to a photoconductive member. The ESV measure the charge applied in an area of test patches in interdocument or interpage zones (IPZ) of the photo conductor. If measured voltages, such as, for example, a discharge area voltage or a cleaning voltage deviate from set point values, level one control loops adjust these xerographic actuators to return the measured voltage to set point. For example, a charge or bias voltage applied to elements of a developer is adjusted to control a resulting development and/or cleaning field. Additionally, or alternatively, a level 1 control loop may adjust a laser power to return a related discharge field back toward a discharge field set point.
Level 2 control loops can include, for example, infrared densitometers (IRD) or enhanced toner area coverage sensors (ETACS) that can measure the density of toner or colorant applied to or developed on a photoconductive member. If the amount of colorant or toner in a test patch is incorrect or varies from a target density, level 2 control loops generate or select one or more new set points for the actuators of the level one control loops.
Level 3 control loops may also use IRD or ETACS sensors. The IRD or ETACS sensors sense actual densities of level 3 test patches associated with a plurality of target level three test patch densities. This provides level 3 controllers with information about actual tone reproduction curves (TRC) and, therefore, with information about residual error between the actual tone reproduction curve and target tone reproduction curves that could not be addressed by the level two control loops. The level 3 controls use this information to build color correction look up tables which are used in an image path to alter image data to compensate for the residual error and obtain the target TRC behavior in a print of the image data.
An operator may adjust any or all of these elements (i.e., machine or system state data) in an effort to achieve a proof image or printing that is approved by a print job customer.
All of these factors make it difficult for an operator associated with a reprint system (whether the reprint system is the same printing system as the system that printed the first or reference printing of a document or a second printing system) to produce a reprint of a document that has a consistent appearance relative to that of a document produced during the reference printing of the document.
Other factors that can have a bearing on reprint consistency include, but are not limited to, environmental factors, such as, temperature and humidity differences, software and color table updates, and operator-to-operator variations in perception.
Accordingly, there is a desire for systems and methods that simplify the reprint proofing and/or printing process and improve consistency in the appearance of reprints relative to earlier reference prints.